The present invention relates generally to a variable displacement compressor, and more particularly to a variable displacement compressor having a suction throttle valve in a suction passage which is in communication with a suction chamber.
A conventional variable displacement refrigerant compressor is disclosed in Japanese Patent Application Publication No. 10-311277 (such type of compressor being referred to merely as “compressor”). In the compressor, lubricating oil in refrigerant gas in the form of a mist is separated therefrom before refrigerant gas under a high pressure is discharged out of the compressor into an external refrigerant circuit. The oil is then collected and stored in an oil reservoir to be supplied to a crank chamber.
In the compressor, lubricating oil is constantly supplied from the oil reservoir into the crank chamber during the operation of the compressor in the entire range from the maximum displacement to the minimum displacement. Thus, lubricating oil may be supplied to various sliding parts of the compressor during the operation at a high speed under a low load in which the flow rate of circulating refrigerant gas is decreased.
For lubrication of the sliding parts, lubricating oil separated from refrigerant gas may be supplied to the crank chamber through the suction chamber.
According to the compressor disclosed in Japanese Patent Application Publication No. 10-311277, however, an excessive amount of lubricating oil is supplied constantly to the crank chamber when the compressor is operated at the minimum displacement thereof. If lubricating oil is stored excessively in the crank chamber, the lubricating oil is agitated at a high speed by rotating parts of the compressor such as a swash plate, so that frictional heat is generated.
The frictional heat thus generated by the agitation causes the temperature of the compressor to rise, which may deteriorate the durability of the sliding parts and various types of seal members made of rubber or resin in the compressor.
To solve the above problem, a suction throttle valve may be provided in the suction passage in communication with the suction chamber. This causes lubricating oil stored in the oil reservoir to be supplied to a region of the suction passage which is located upstream of the suction throttle valve. When the compressor is operating at the minimum displacement or stopped, the suction throttle valve is closed. Thus, lubricating oil supplied from the oil reservoir is stored in the region of the suction passage upstream of the suction throttle valve, so that lubricating oil is hardly supplied to the crank chamber. In the above structure, the operation of the compressor is changed from the maximum displacement to the minimum displacement or to a stopped state, and then the compressor operation is changed to the maximum displacement again in a short time. In this time, refrigerant gas in the crank chamber whose pressure is increased during changing the operation to the minimum displacement flows toward the suction chamber through a gas flow passage. Since the suction throttle valve is then closed, the refrigerant gas has no way to flow. Thus, the crank pressure cannot be reduced rapidly. Therefore, it may take a long time until the crank pressure is reduced to a predetermined desired pressure when the operation of the compressor is changed to the maximum displacement.
The present invention, which has been made in view of the above problems, is directed to a compressor which prevents lubricating oil from being supplied to the crank chamber excessively, and is operated to return to the maximum displacement smoothly.